Process for the purification of magnesium chloride



May il, 1945; 7 R. LEPso LAL 2,3.75.1309` PROCESS` FOR THE PURlFIGATIONOF-MAGNSIUM lCHLORIDE- Filed Jan. 2l, 1941 Rca-ber* Lefaog Basil GrahamH'u-rln-f Piante# Mey s519455,

01H*ICE,il f

v MAGNESIUM CHLORIDE y RobertLepsoeand Basil Graham Hunt, Trail,

y `British Columbia, Canada,` assignors,.by mesne v l,

l, assignments, to The Mathieson Alkali Works ,A (Ina), a corporation ofVirginia j 1 In Canada February 7, 1940 sciame. (Cram-,roi

This inventionrelatesto aA process for the puri ilcation of @moltenvmetalchlorides Aand is more specically vdirected to providing a 'simpleandv highly eflective `rneiahodforl the puriilcationl of anhydrousmagnesium chloride in the molten state, A t; y Processes for `theelectrolysis of molten magnesium rchlorideP-tol obtain metallicmagnesium therefrom have-been in relatively'widespread use` for manyyears past. It isalso well known that ma'gnesite (magnesium carbonate),whichoccurs in'nature `alone or in compounds such as 'do1o` mite(MgCOaDACQs), can be converted into chloride form and the resulting`magnesium chloride electrolyzed to recover the metallic magnesiuminsubstantially pure form.

For theV successful electrolytic separation of magnesium from moltenmagnesium chloride electrolytes, the magnesium chloride must besubstantially free from suspended solid impurities such as' carbonsilica and magnesium oxide, or

soluble impurities suchfas iron and* aluminum. in'chloride form, rwhichmetals are below mag# nesium in the-electromotiveseries. Preferably,

the magnesium chloride should contain no water and a total oi notmorethan y1% of suchimpurities.` Magnesium chlorideof this quality issultable for direct addition to the electrolytic oell and recoveriesofthe order of 90% ofthe magnesium,

with high current eillciency, can be4 obtained. .To

illustrate-theimportance of using amagne'sium chlorideelectrolyte-substantially free, fromv lm-v purities,'including water,whichlatter tends to reactwith magnesium chloride'por Imagnesiummetal,orbot h, to, form/magnesium oxide,- itis found; that-la recoveryofonly yabout 80 %f of the magnesium can be-. obtained `from magnesiumchloriile containing. 2%- impurities, while a ree covery ofonly-6,0%canv be,A obtained fromimag.- 1

nesium chloridey containing 4% impurities. -These lowerrecoveries aredue ,to/theretention of electrolyte and of metallic magnesiumv `bymagnesium oxide and-Miller4 insoluble impurities, which form mud inthecell'and which it isnecessary to re-vv move fromthe electrolytic cellduring operation. Magnesium chloridey mayberobtained by chlorinatingmaterials such as magnesite (MgCOa),v

or dolomite (MgCO:.CaCOa), in the presence of carbon. Magnesium chlorideprepared in such a manner usually contains, in addition to a smallamount o! moisture, small amounts'oi' other impurlties auch as magnesiumoxide. silica -and carbon in the form of suspended solids, and iron.mmlnllm Ind nnlnlnm In L .u- -1 1 un of metallic magnesium, accompaniedyby a high current eillciency` in;the;, subsequent electrolytlc step.Y Y

In order to eilect'the separation-of the sus' pended vsolid impurities,such as magnesium oxide, silica `and carbon, it hasbeen suggested to fpass the. fresh, incoming molten magnesium chloride through a settlingfurnace wherein the suspended solid impurities arey permitted to settleto the bottomrof the furnace,lthe magnesium chloride being thenrseparated therefrom by such means as decanting This treatment .may becontinued through several settling furnaces until the substantiallycomplete separation of solid impurities has been eii'ected. vIn suchprocesses, no procedure is suggestedior separating the solubleimpurities, `such as iron,l aluminumand calcium, which are present in;chloride form and whic'h,1 for `the most part, remain ywith the fmoltenmagnesium chloride andi/pass to the electrolytic cell.

Electrolysis may be carried-out in l one or a series of cellscontaining. positivefand negative electrodes, or in a vmetal .poux suchas caststeel, in which the metal shellacltsas thervn'egative electrodeor cathode `and avertical,centrallylocated electrode serves as the.positive electrode or anode.'

Duringelectrolysi's. chlorine formed at the anode and mayv be recovered,ifA so. desired, kand returned ,to thechlorinating zstep `of theprocess, while molten magnesium metal. is `folrxned at the.

feathode and; beingj lighter than the molten"11mg-k valentA dquantity of'magnesium oxide which, to-

gether with the silica, carbonV and'magne'sium oxide already present finthe electrolyte, settlesj to the bottom of the cell Yas mud? A portionofthechlorides of iron andraluminum may be gvolatilized; the.ir`o`nandaluminum content of the remaining portion precipitated by themagnesium metal present in the electrolyte. It will be seen that thepresence ofthe metal chloride impurities in the electrolyte is veryundesirable due to their deleterious eil'ect upon the quantity ormetallic magnesium recovered, and upon the current emciency, besidesincreasing' The mud. formed d uring electrolysis, settles to the'bottomof the cell and a portion of the mnsneslum metal produced bytheelectrolysis is entralned by this mud. Under these conditions, anappreciable percentage of metallic magnesium is foundin the mud andremoved with it. The percentage of magnesium metal thus recovered withthe mud is dependent mainly upon the extent to which impurities arepresent in the original chlorid e fed to the electrolytic cell and, tosome extent,

also, cnthe amount oi' impuritiesgsuch as magnesium oxide and carbon,which may enter the electrolyte during electrolysis. l

It has been found that the purification of the freshly preparedlmagnesium chloride, which may contain small amounts of impurities, suchas moisture, magnesium oxide, silica, carbon,

iron, aluminum and calcium, can beaccomplish- -f ed in a simple,inexpensive and highly effective manner by treating the magnesiumchloride in an externally or internally heated purification furnace. Itis preferred to maintain the temwithin the range of from '125 C. to 775C., the charge being sufilciently iluld and theloss of magnesiumchloride through volatillzation being negligible within this temperaturerange. Mud, withdrawn from the electrolytic cell, containing up to about10% metalic magnesum, together with varying percentages of magnesiumoxide.

silica, carbon, iron, aluminum and entrained perature of the chargecontained in this furnace sheet. In the modificationillustratedin-Pigure' 1, the puriilcationtreatment and the' complete:separation ofthe solid and precipitated impu'rlinasmuch Las calcium isabove magnesium in the -electromotive series, it remains with the moltenpurled chloride passed to the electrolytic cell. The calcium originatesin the calcium oxide which is present in the charge fed into thechlorinating and the chloride produced there.` from contains all thiscalcium. As the electrolysis of the vmolten chloride proceeds, thecalcium content of the electrolyte gradually builds up to vs,

point at.y which the electrolyte must be discarded.

The impurities precipitated from the fresh. molten magnesium'chloride bythe action 'of the metallic magnesium, togetherwith all the insolubleimpurities of the mud and of the fresh magnesium-chloride, settle to thebottom of the lluri-v iication. furnace, from .which they may lberemoved periodically. Metallic magnesium, in. ex.

cess of that 'required for the reactions, collects at the surface of thebath, :from which it may be removed.' or 'passed tothe electrolytlc cellwith the purified chloride. v

The purinedmagnesium `chloride may be pass` ed directly to theelectrolytic step of the process or to a second holding or'settlingfurnace, from which itisV withdrawn, as required, and passed to theeiectrolytlc cell. r-

The, mud and precipitated metallic impurities.

vsettlingto the bottom of the puriilcation furnace,

are removed periodically by a perforated ladle or other suitable means,and may be leached with water to dissolve and recover magnesium chlorideor may be treatedby other means for the ref..

covery of the metalvalues.

The following analyses are illustrative of the manner in which themetallic magnesium. con-` tained in the-mud withdrawnl from electrolyticcell, is edective in precipitating metallic impurities from the moltencharge, and ofthe man ner in which the chloride is puriiled:

Per Per Per wPer `Per cant M cent amt cent. cent MgO 510| Al i Re C lChlorideclmgetopurlileatloniumace 0.7 0.4 0.1 0.2 0.6 Pm'iedehloride 0.10.1 Trace 0.l 0.01

It has been found possible, by the method' dlsclosed vhereixiil.bove,.topurify the molten=cliioii(ieA charge to such an extent that, on

into the electrolytic cell, it is i'reey from the impurities. moisture,magnesium oxide.

carbon. silica, iron, and aluminum, 'auch' other metallic impurities asmay bebelow inail-l nesium inthe electromotive series. -ifiliicli im'fpurities were either-all or in part present. in theE charge originallyfed into the purillcation-furnace, o'r were picked up subsequently.- In.this manner, it is possible lto improve the operation of the cell. thecurrent eiilciencyandltlie metal recovery.

y Alternative-methods for carrying. outthe pres- A ent invention areillustrated in the attached-now tiesare elfected in the'puriflcatlonsettling furnace. In the modification illustratidj'lnllgure 2. thepurification treatment and'tiieseparationof a portion of the solid andprecipitated' impurities are effected in the purificationsettling-furnace', after which the fused chloride is passedto a settlingfurnace wherein the remainder ofthe solid and precipitatedimpurities Itwinne-clearly examples usedA hereinabove to illustrate .the operation ofthe method'are-not tobe construed as limitlng'the scope of the inventionaalfdeilned in the appended claims.

What we claim as new and desire to'protect by.

Letters Patent of tl'ieUnited States is:

1.- m a process for the-electrolysis production magnesium of metallicmagnesium fromy fused chloride electrolyte. the methodof purlfyingthemagnesium. chloride electrolyte' prior to elec-- trolysis whichcomprises charging the magnesium chloride into a purification furnacemaintained at a temperatureabove the melting temperature ofthe chargecontained therein, addlngto the molten'charge cell mud withdrawn fromthe electrolytic stepof the cell mud containing entrained metallicmagnedum, the metallic magnesium causing precipitation of the solublemetalimpurities-which arebelowmagnesium in the electromotive series ofthe elementsvand which are present in the-magnesium chloride:permitting. the impurities, including those whichare precipitated by themagnesium metal contained in the cell mud. t0 settle as mud to thebottom of the purificationl furnace.- and' separately withdrawing thepurified magnesium chloride electrolytefand the-settled mud.v

2. In a process lor the electrolytlc production `of .metallic magnesiumfrom fused magnesium' chloride electrolyte, the method oi' purifying thechloride electrolyte prior to electrolysis which the magnesiumunderstood, of theA chlorideinto a purification furnace maintained atincluding those'which are precipitated by the magnesium metal containedin the cell mud, to settle as mud to the bottom of the purificationfurnace, separately withdrawing the fused magpresent in the magnesiumchloride; permitting, a portion of the impurities, including those whichnesium chloride and the settled mud, -passng the fused magnesiumchloride to a settling furnace wherein the remainder of the suspendedimpurities are permitted tol settle, and separately withdrawing thepurified magnesium chloride electrolyte and the settled mud from thesettl'ng furnace.

3. In `a process for the electrolytic production' of metallic magnesiumfrom fused magnesium chloride electrolyte, the method of purifying themagnesium chloride yelectrolyte prio-r to electrolyr sis which comprisescharging the magnesium chloride into a purification furnace maintainedat a temperature within the rangeyof from 725 C. to

'17.5 C., adding to the molten charge cell mud separately withdrawn fromthe electrolytic step of the process, said cell mud containing entrainedmetallic magnesium, the metallic magnesium causing the precipitation ofthe soluble metal impurities which are below magnesium in the electromotive series of the elements and which are present in the magnesiumchloride; permitting the impurities, including those which areprecipitated by the magnesium metal contained inthe cell mud, tosettle'as mud to the bottom of the purification furnace, and separatelywithdrawing the purified magnesium chloride electrolyte and the settledmud.

4. Ina process for the electrolytic production of metallic magnesiumfrom fused magnesium chloride electrolyte, the method of purifying themagnesium chloride electrolyte prior to lectroly- Patent Sno. 2,575,009.

CERTIFICATE or coRREcTIoH.

ROBERT LEPSOE, ET AL.

sis which comprises charging the magnesium chloride into a purificationfurnace maintained at a temperature within the range of from 725 C. to'775 C., adding to the molten charge cell mud separately Withdrawn fromthe electrolytic step of the process, said cell,mud containing entrainedmetallic magnesium, the metallic magnesium causing the precipitation ofthe soluble metal im' purities which are below magnesium in theelectromotive series of the elements and which are arevprecipitated bythe magnesium metal containedin the cell mud, to settle as mud to thebottom of the purification furnace, separately withdrawing the fusedmagnesium chloride and the settled mud, passing the fused magnesiumchloride to a settling furnace wherein the remainder ofthe suspendedimpurities are permitted to settle, and separately withdrawing thepurified magnesium chloride electrolyte and the settled mud from thesettling furnace.

l 5. Ina process for the electrolytic production of metallic magnesiumfrom fused magnesium chloride electrolyte, the method of purifying themagnesium chloride electrolyte prior toelectrolysis which `comprisescharging the magnesium chloride into a purication furnace maintained ata temperature above the melting temperature of the charge containedtherein, adding to the molten charge a metal chloride, selected from the(group consisting of sodium chloride and potassium chloride, and cellmud separately Withdrawn from the electrolytic step of the process, saidcell mud containing entrained metallic magnesium,

Hay 1, k19145.`

It-ie Vhereby certified thatierror appears in the printed specificationof the ebove'fnumbered patent requiring correctioxlas follows z Page 1,first column, 11m 15, for thefom1e-(ngco3.cico5)" read (ngco5.cnco5);page 2, first column, line 29, for "mettallcfmegnesum" read #metallicmagnesium'n; and that the seid Lettere Patent should be read with thisvcore rection therein thetkthe 4naine mq `'conform Patent4 Office.

to therecord of the case in the y l(Seul) Leslie Frazer Actingnmieerlioner of Potente .f

chlorideinto a purification furnace maintained at including those'whichare precipitated by the magnesium metal contained in the cell mud, tosettle as mud to the bottom of the purification furnace, separatelywithdrawing the fused magpresent in the magnesium chloride; permitting,a portion of the impurities, including those which nesium chloride andthe settled mud, -passng the fused magnesium chloride to a settlingfurnace wherein the remainder of the suspended impurities are permittedtol settle, and separately withdrawing the purified magnesium chlorideelectrolyte and the settled mud from the settl'ng furnace.

3. In `a process for the electrolytic production' of metallic magnesiumfrom fused magnesium chloride electrolyte, the method of purifying themagnesium chloride yelectrolyte prio-r to electrolyr sis which comprisescharging the magnesium chloride into a purification furnace maintainedat a temperature within the rangeyof from 725 C. to

'17.5 C., adding to the molten charge cell mud separately withdrawn fromthe electrolytic step of the process, said cell mud containing entrainedmetallic magnesium, the metallic magnesium causing the precipitation ofthe soluble metal impurities which are below magnesium in the electromotive series of the elements and which are present in the magnesiumchloride; permitting the impurities, including those which areprecipitated by the magnesium metal contained inthe cell mud, tosettle'as mud to the bottom of the purification furnace, and separatelywithdrawing the purified magnesium chloride electrolyte and the settledmud.

4. Ina process for the electrolytic production of metallic magnesiumfrom fused magnesium chloride electrolyte, the method of purifying themagnesium chloride electrolyte prior to lectroly- Patent Sno. 2,575,009.

CERTIFICATE or coRREcTIoH.

ROBERT LEPSOE, ET AL.

sis which comprises charging the magnesium chloride into a purificationfurnace maintained at a temperature within the range of from 725 C. to'775 C., adding to the molten charge cell mud separately Withdrawn fromthe electrolytic step of the process, said cell,mud containing entrainedmetallic magnesium, the metallic magnesium causing the precipitation ofthe soluble metal im' purities which are below magnesium in theelectromotive series of the elements and which are arevprecipitated bythe magnesium metal containedin the cell mud, to settle as mud to thebottom of the purification furnace, separately withdrawing the fusedmagnesium chloride and the settled mud, passing the fused magnesiumchloride to a settling furnace wherein the remainder ofthe suspendedimpurities are permitted to settle, and separately withdrawing thepurified magnesium chloride electrolyte and the settled mud from thesettling furnace.

l 5. Ina process for the electrolytic production of metallic magnesiumfrom fused magnesium chloride electrolyte, the method of purifying themagnesium chloride electrolyte prior toelectrolysis which `comprisescharging the magnesium chloride into a purication furnace maintained ata temperature above the melting temperature of the charge containedtherein, adding to the molten charge a metal chloride, selected from the(group consisting of sodium chloride and potassium chloride, and cellmud separately Withdrawn from the electrolytic step of the process, saidcell mud containing entrained metallic magnesium,

Hay 1, k19145.`

It-ie Vhereby certified thatierror appears in the printed specificationof the ebove'fnumbered patent requiring correctioxlas follows z Page 1,first column, 11m 15, for thefom1e-(ngco3.cico5)" read (ngco5.cnco5);page 2, first column, line 29, for "mettallcfmegnesum" read #metallicmagnesium'n; and that the seid Lettere Patent should be read with thisvcore rection therein thetkthe 4naine mq `'conform Patent4 Office.

to therecord of the case in the y l(Seul) Leslie Frazer Actingnmieerlioner of Potente .f

